MORE AND MORE high school graduates show up in college classrooms, employers' personnel offices, or at other common checkpoints with barely and no writing facility at all." That lament comes from Willard Wirtz and his colleagues, reporting on the long decline in the Scholastic Aptitude Test scores. Every year the test is taken by a million high school students on their way to college, and the decline has been continuous since 1963. The College Entrance Examination board asked Mr. Wirtz, the former Secretary of Labor, and his committee to see what was going wrong. Their report offers an interesting diagnosis.

The test is cultural weathervane of exquisite sensitivity, picking up all sorts of currents - both in the classroom and far beyond it. Some of the causes of the lower scores can be demonstrated statistically. The first part of the long slide, up until about 1970, resulted mainly from the increases in the numbers of youngsters going to college. More kids from poor families were taking the test and, in the broad average, students from poor families do less well than those from more prosperous homes. More blacks took the test, and racial discrimination in the past affects academic performance in the present. Women score markedly less well than men in the mathematical section of the test (although as well, or slightly better, in the verbal section). As the proportion of women rose among the students taking the test, there was an impact on the average math score.It's due to the tradition that steers women away from careers in mathematics and science, the committee thinks.

But that's clearly only half of the explanation. After 1970, the social balance among the students taking the test did not change much. Yet the decline in test scores continued steadily. Why?

Here much of the answer has to be speculation - but the speculation is plausible. The Vietnam war and political turmoil created, the committee suggests, a "decade of distraction." A great many young people withdrew into a separate world of their own. It also seems likely that the nationwide epidemic of juvenile addiction to television may have had a part in lowering the test scores.

But at the same time, much more specific things were happening in the schools. If there is a remedy, that is where it lies. To take one example, Mr. Wirtz and his committee note that in the Massachusetts schools a great variety of electives suddenly began replacing the English courses - the most common of the electives being Science Fiction and something called Radio/Television/Film. The schools with the largest enrollments in those two particular courses also turned out to have had larger than average declines in the college entrance test scores. Throughout the country the words and sentences in textbooks got shorter. Absenteeism rose, and teachers increasingly tolerated it. The Wirtz committee concludes that, in general, there has indeed been a decline in educational standards.

"We attach central importance to restoring the traditions of critical reading and careful writing," the committee says. Exactly so. From the Sputnik reaction of the late 1950s, with it emphasis on physical sciences and foreign languages, the schools - in the great national tradition - swung heavily to the other extreme. It was suddenly a time of romantic and experimental ideas: what counted were feelings and experience, rather than information and reasoning.

The time has come to begin moving forcefully in another direction, and our sense of it is that the march is already under way. In some of the Washington area's high schools, the college-bound students are once again being firmly introduced to Beowulf, not because he's amusing but because they need to know about him. More students are again writing formal papers. The Wirtz committee's recommendations will serve to strengthen such welcome changes. The report notes that the test scores' rate of decline has slowed. But it hasn't stopped. This year's scores, published yesterday, are once again a couple of points lower than last year's.

The purpose of education is not merely to passtests. But this particular set of tests ia a broad and accurate gauge og students academic competence.That competence is a substantial part of the national wealth, and a persistent drop from year to year is not a thing to be tolerated